Proton exchange membrane (PEM) fuel cells are useful due to their high energy density, high efficiency, relatively low operating temperature and low emission of pollutants.1 However, low performance of the oxygen reduction reaction (ORR) at the cathode is a principle obstacle to the successful application of PEM fuel cells, particularly in transportation. Various Pt based alloy catalysts2-8 have been developed and show enhanced catalytic activity compared to Pt/C towards oxygen reduction reaction in PEM fuel cells, and also in phosphoric acid fuel cells that operate at higher temperatures. Nevertheless, in most of the methods9-11 for preparation of carbon supported Pt-based alloy catalysts, high temperature (e.g., over 900° C.) is required to form the alloy, resulting in a lower catalyst active area.9 Another disadvantage of such methods is that the Pt and other transition metals may deposit separately on the carbon support, rather than in close association.
The enhancement of ORR electrocatalytic activity in lower temperature PEM fuel system was reported17-19 based on an investigation of a series of five binary alloys with Pt using the first row transition elements ranging from Cr to Ni. These results have been summarized in several reviews.20,21 Further confirmation of enhancement in activity for ORR in PEM has been reported using supported Pt alloy electrocatalysts in a PEM fuel cell22,23. The role of alloying element in engendering enhancement of ORR catalytic activity in Pt based alloy catalysts has been ascribed to a decrease of the desorption free energy (ΔGads) of oxide species on Pt, particularly OH.
There remains a need to develop new synthetic methods for making carbon-supported platinum alloys with predictable and controllable crystal structure and surface composition so as to improve the performance of cathodic catalysts and the kinetics of ORR in PEM fuel cells.